Typical prior art sensing edges generally include a sheath having a cavity along the length thereof wherein at least a portion of a switch is located. The sensing edge is attached to an edge of a door which may be moved in different directions. When external pressure is applied to the sheath of the sensing edge the switch is activated to actuate a door control device which causes the door to either stop moving or open. For example, external pressure may be applied to the sheath when the sheath contacts an obstructing article, such as a body of a person, located between the sensing edge and an opposed surface. By stopping or changing the direction of movement of the door, damage to the obstructing article may be prevented.
In prior art sensing edges, the switch generally includes first and second electrically conductive contacts positioned on opposed foam layers within the cavity and spaced apart from each other. When the sensing edge contacts an obstructing article, the portion of the sheath contacting the obstructing article is deflected to cause the first and second contacts to engage and make electrical contact therebetween. The door control device, which is electrically coupled to the first and second contacts, monitors in some manner the first and second contacts. Upon detecting engagement between the first and second contacts, the door control device causes the door to either stop moving or to open.
However, it may not be possible for the door control device to detect engagement between the first and second contacts if electrical problems (such as open circuits or short circuits) exist in one or both of the first and second contacts. As those skilled in the art will appreciate, articles which obstruct the downward movement of the door will be damaged unless such electrical problems in the first and second contacts are immediately detected and acted upon.
Some prior art sensing edges assist in providing a means for detecting electrical problems in the first and second contacts. In other words, some prior art sensing edges assist in providing a failsafe feature to detect electrical problems in the first and second contacts. Typically, such prior art sensing edges include first and second wires connected to the ends of the first contact and third and fourth wires connected to the ends of the second contact. The first, second, third, and fourth wires are relatively long in length and are positioned through long lengths of the cavity, such that the first, second, third, and fourth wires are accessible from outside of the sensing edge. A door control device, which is located outside of the sensing edge and which is electrically connected to the first, second, third, and fourth wires, can detect electrical problems in the first and second contacts by measuring the resistance, current, voltage, etc., existing between the first, second, third, and fourth wires.
Although they assist in providing a failsafe feature for detecting electrical problems in the first and second contacts, such prior art sensing edges are typically time-consuming and difficult to assemble because the first, second, third, and fourth wires must be positioned through long lengths of the cavity and secured therein to the first and second contacts. Also, since they are very long in length, the first, second, third, and fourth wires are themselves subject to electrical problems.
Therefore, it would be advantageous to have a sensing edge which assists in providing a failsafe feature to detect electrical problems in the first and second contacts of the sensing edge, wherein the sensing edge is relatively easy to assemble, and wherein the possibility of electrical problems occurring in the failsafe feature itself is minimized.